Using current “on the shelf” technology how long would it take to reach the nearest star for a robot probe?
here’s one answer…
http://image.gsfc.nasa.gov/poetry/ask/a10667.html
There was a better link that I can’t find at the moment unfortunately. Different types of propulsion may cut the travel time somewhat (e.g., ion propulsion), but there’s still no getting there in our lifetime.
Well, Robert Forward has designed his Starwisp probe…essentially a photon sail powered by lasers from our solar system. The catch is that you use a very very small payload…the whole probe including sails is only a few kilograms. We’ll need some advances in nanocomputing for this to be useful. You can get the probe home again by using the main part of the photon sail as a mirror and reflecting the laser back to a small portion that contains the “data recorder”. The problem of aiming and focusing the laser propulsion system over light-year distances is left as an exercise for the reader. But this isn’t quite using existing technology, we’d need several advances for this to work.
OK, find out the speed of the fastest interplanetary probe. Divide by the distance to the nearest star. There’s your answer.
But don’t forget relativistic effects…the faster you go, the shorter the trip seems to you (compared to the observer using that equation back on Earth).
Aren’t we close enough to a star now? Personally, I like the sun right where it is, even though it is a bit hot today.
I think he meant the NEXT closest star, BobT. 
Voyager 1 is humanity’s fastest space probe, retreating from the sun at 17 km per second. If it was heading towards the nearest star (although it is not), Alpha Centauri, it would require 90,000 years to get there. Even if a space probe could travel at one percent of the velocity of light, a speed enormously faster than any current technology, the voyage would still take 440 years.
Alpha Centauri’s distance is 42 trillion km, or 4.4 light years.
Years ago I had a sweet book on space technology (I think that might have been the title) which had a proposal for an extrasolar mission. As the book is now twenty years old, I think that the “projected technology” has pretty much caught up–most of the necessary technology was in materials and AI.
The main objective was to be able to get a vehicle built and launched in such a fashion that successful mission results would return within the builders’ lifetimes. The design itself resembled two enormous bells. It’s “fuel” was two holds of nuclear bombs. The bombs were to be dropped into the focus of the parabolic firing chamber and detonated.
The thing would just go along, boom, boom, boom, until it reached about eight percent of the speed of light (I think), then it would cruise for a long, long time. As it approached Alpha Centauri, it would jettison the first bell section, spin about, and repeat the process with the smaller section.
It would slow down enough for some pretty serious data to be collected and beamed back, but it would still be going very fast, and would pass straight through the heart of the system in a matter of days. Then we’d just have to wait for the signals to return to earth–about three years or so.
Total mission time: 60 years, if I recall correctly.
Incidentally, while the Voyager spacecraft (and a couple of Pioneers before them) are now beyond the orbit of Pluto, I’m not certain they have actually achieved escape velocity from the Sun. I remember reading once that the only rocket ever successfully used which could (potentially) send a payload to another solar system was the Saturn V; it supposedly could deliver a fourteen-pound package to Alpha Centauri in a few hundred, or perhaps thousand, years.
I don’t know, maybe those probes picked up a lot of speed in their gravity assist maneuvers.
The book Footfall, by Larry Niven and Jerry Pournell (the greatest science fiction team ever to grace the pages of paperback) contains a nuke propelled ship such as you have mentioned. It was, IIRC, based on some actual government research at some point.
However; there are a coupla problems with that concept. First, Can you imagine how huge and heavy a ship would be that could withstand a nuclear blast and use it as propulsion? My WAG is that the bell would have to be at least 2-3 meters thick of hard steel (or maybe tungsten, with a higher melting point)
We could build such a craft, although it would be enormously expensive, but we could never, by any feasible means, get it into orbit. In the book, they solve that problem by using the same nuclear propulsion system to launch it as to propel it between the stars. In the process, they reduce a good portion of Washington to radioactive rubble (But they HAD TO. They had to fight off the space invaders!).
Any volunteer cities to host such a project?
But think of the jobs it will create, the money which will flow into the local economy! Not just from the project itself, but longer term, cleaning up after it. And this doesn’t even count the tourist dollars…
Seems like current ideas focus more on (1) ion propulsion (2) solar sails (3) laser sails (4) anti-matter propulsion
I read somewhere that they could build an Orion-type vessel that could get someone to Alpha Centauri in 50 years with the equivelant of 3 years U.S. military budget. This was several years ago, though…
Let’s say that we do reach Alpha Centauri in our lifetime. Would it be a big ball of gas like our sun? Or would it be a planet?
From the official Voyager website: "The Voyager spacecraft will be the third and fourth human artifacts to escape entirely from the solar system. Pioneers 10 and 11, which preceded Voyager in outstripping the gravitational attraction of the Sun, both carried small metal plaques identifying their time and place of origin for the benefit of any other spacefarers that might find them in the distant future. "
Alpha Centauri A and Alpha Centauri B are both main-sequence stars (and hence big balls of gas); Alpha Centauri A is a G-type star (the same as the Sun); B is a bit cooler. Proxima Centauri, the last member of the trinary system (at a considerable distance from the other two), is a smaller red dwarf, but it’s still a star. It’s not clear if a binary system can have planets or not.
FTR, Proxima probably isn’t part of (i.e., gravitationally bound to) the Alpha C binary. They seem to be a bit older than the Sun (for one thing, they have lower metallicities), whilst Proxima is a flare star (which, in class M dwarfs, implies than it’s younger than the Sun). It’s probably just cruising by.
Also, there’s no question that a binary can keep planets once they are formed (I believe that that was shown in the 19th C). I think that planets (or something that seems like a planet from back here) have been detected around some binaries, but whether the average binary (or multiple) sucks up the gunk that would become planets during its formation is still open to question.
[Seems like current ideas focus more on (1) ion propulsion (2) solar sails (3) laser sails (4) anti-matter propulsion]
don’t forget about nuclear propulsion where a nuclular reactor superheats gas instaed of burning it
:rolleyes:
Why the look? He’s right.
As you accelerate towards the destination, the distance, from your perspective, contracts. Therefore, from your perspective, your trip takes less time than an outside (non-accelerating) observer.
Say you’re going to a star 4 light-years away, and that you have the technology to accelerate to 99% of the speed of light. The Lorentz gamma is 1/sqrt(1 - v[sup]2[/sup]/c[sup]2[/sup]), so, from your perspective, the distance now appears to be one-seventh of that. So, instead of it taking ~4 years, that someone staying on Earth would see, it takes about 7 months for those making the journey.
That’s where the “twin paradox” comes from. The twin who travels out and back near the speed of light experiences less time than the twin who stays there.
Arg. Yes, he’s right, BUT we are talking about off-the-shelf tech here…if you are traveling at less than 10% of c during your trip, only an accurate clock will tell the difference. OK, maybe the time dilation would be measured in minutes at that velocity…(my firm policy is to always let other people do the math or look up the links…) but it would still be a neglibile fraction of the trip time. If you were up to 90% c, then we’ll worry about relativity.
If we’re talking about strict off the shelf, the trip will take thousands of years. If we’re being more generous and include stuff that we know how it would work even though no one has ever built it, the trip will still take decades.
The trouble with going at very high percentages of c is not the power source, we can very easily imagine an antimatter reactor that converts 100% of the energy of combining matter and antimatter into heating the reaction mass. The trouble is carrying around the reaction mass. It doesn’t matter how hot you get the stuff, there’s a limit to how much delta-v you can carry around. OK, you can add extra fuel tanks, but pretty soon you’re spending all your reaction mass on accelerating the reaction mass. That’s why all those Larry Niven fusion ships or Heinlein torchships won’t work. Your fusion reactor/torch can blaze away for eternity, but you’re still stuck with the old “throw the rocks off the back of the canoe” rocket paradigm.
So most current ideas try to get around this by designing photon sails, or such. Of course, you can postulate reactionless thrusters or antigravity or hyperspace and get to Alpha Centauri any time you like. But I’m assuming we’ll stick to known physical laws for now.
For someone who’s read so much Science Fiction you have no hope for the future.
Why not build it in orbit? That’s how they’re doing the international space station, and that thing is big. You could bring it up piece by piece, put it together, put some rocket engines on it and aim it away from the Earth. When it gets far enough away, press a button and BOOM! off it goes.